1. Field of the Invention.
The present invention relates to gaskets, and in particular to a motorcycle engine cylinder base gasket having a perimeter bead seal.
2. Description of the Prior Art
Internal combustion engines of various kinds are well known in the art. For sealing a clearance between the surfaces to be sealed, e.g. a cylinder and a crankcase block of an internal combustion engine, various gaskets are deposited therebetween. The gasket for use on the internal combustion engine defines a plurality of openings, e.g. the bore opening and fluid (oil) openings and clamping stud holes, and is clamped between the cylinder and crankcase so that oil or other fluids will not spread from these openings.
Internal combustion engine gaskets can be made from paperboard, cork, rubber, metal or other flat material. The high temperatures and corrosive materials (such as oil and gasoline) found in an engine will cause paperboard, cork and rubber gaskets to deteriorate resulting in gaps which lead to fluid leaks.
The constant vibration of a motorcycle engine can cause paperboard, and cork gaskets to compress unevenly between the metal parts of an engine. The short-term solution to this problem is to apply more torque to the gasket by tightening the metal engine parts around it. However, such gaskets do not retain such torque so that within a relatively short period of time, the vibration of the engine will loosen the gasket, which can lead to leaks in the uneven gaps.
An oil leak in a small motorcycle engine can be particularly dangerous since the engine runs at a very high temperature and does not hold much oil in the first place. A motorcycle engine can be severely damaged and malfunction before such a leak is even detected. As a result of these factors, among others, paperboard, cork and rubber gaskets must frequently be replaced.
Metal gaskets generally do not deteriorate in the same way that paperboard, cork or rubber gaskets do. However, a metal gasket does not necessarily provide a leak-proof seal because it is not pliable in the same way that paperboard, cork and rubber gaskets are. Metal gaskets made of copper are particularly dangerous because if placed between opposing engine parts made of aluminum and iron, a chemical electrolysis takes place which may erode away the copper of the gasket. Constant replacement of gaskets is expensive and time consuming.
No two motorcycle engines are exactly alike, and each will have its own good and bad fitment characteristics. Some engine manufacturers are notorious for providing engine parts that do not fit together well. It is not at all uncommon for a motorcycle engine crankcase to have an uneven surface at the cylinder base where the two halves of the crankcase are bolted together. Similarly, the mating surface of the cylinder itself may not be uniform or flat. Other potential poor fitment situations include rocker cover gaskets, cylinder head gaskets and oil pan gaskets. In such situations, the function of a gasket becomes even more important since there may be relatively large gaps between the metal parts which must be sealed.
In particular, Harley-Davidson 1340 cc V-Twin motorcycle engines made between the years of 1984 and 1996 have machining variances of several thousandths of an inch between the crankcase halves. Harley-Davidson engine crankcases split into a left and right side rather than top and bottom halves leaving a small step at the mating surface. When the cylinder is installed onto the assembled crankcase, the uneven crankcase mating surface makes fluid sealing difficult.